Turbine engines include one or more combustors, each provided with one or more main fuel injectors for injecting fuel during normal operation of the engine and often, particularly in small engines,one or more start injectors which inject fuel while the engine is being started. These injectors include nozzles or outlets that are disposed within the combustion space of the combustor and which may include very small orifices in order to obtain a desired atomization of fuel upon injection.
Inasmuch as the orifices or outlets are within the combustor, they are exposed to substantial heat. During normal operation, this does not present a problem because the flow of fuel to the injector provides a cooling action and the propagation of combustion along with the flow of oxidant will prevent undesirable overheating of the injectors.
When operation of the turbine is terminated, fuel no longer flows through the fuel injector to cool the same. Similarly, oxidant is no longer passed into the combustor and the cooling action of the oxidant is no longer available. Consequently, residual heat in the combustor ar of the engine will cause elevation of the temperature of the fuel injectors. In terms of the material of which the injectors are formed, this raising in temperature upon cessation of operation of the turbine does not present a problem. However, the presence of residual fuel in the injector at such time will frequently cause a so-called coking problem. Being carbonaceous in nature, such fuel, upon being heated, will begin to undergo a destructive distillation reaction and a coke-like or and/or tarry residue will remain. This residue will clog the injectors and result in improper operation on subsequent start-ups.
Consequently, the injection system of turbine engines has been purged of fuels following shut-down to prevent coking from occurring and thus prevent clogging. In some cases, the purged fuel is dumped overboard. See for example, U.S. Pat. Nos. 2,846,845 and 3,426,527. In other cases, the fuel being purged is collected in a tank or the like. See U.S. Pat. Nos. 3,841,089 and 3,901,025.
While both approaches serve the purpose, the former is undesirable in that it requires a certain amount of plumbing to convey the fuel to be purged to an overboard point of discharge. The latter is even more undesirable because it will require some sort of a purge bottle which may be bulky and of substantial weight, and involves added complexities of valves, relief valves, check valves, etc., factors that are particularly disadvantageous in aircraft turbine installations.
In order to overcome these and other problems, there is disclosed, in the previously identified patent application of Shekleton et al, an improved fuel injection system including provision for purging of the same. This system works well for its intended purpose; and the present invention is directed to improving upon it, primarily in terms of simplifying system components and/or reducing the number of system components so as to minimize the cost of taking advantage of the efficiency accompanying use of that system.